Statistical Characteristics of Short-time Heavy Precipitation in Shan-Gan-Ning Region from May to September in Recent 6 Years

The statistical characteristics of short-time heavy precipitation vary in different areas. Based on thehourly automatic weather station precipitation data and NCEP reanalysis data with the resolution of 1°× 1° in Shaanxi, Gansu, Ningxia from May to September during 2005—2010, the statistical analysis are conducted to explore the spatial-temporal distribution of short-time heavy precipitation in different class, synoptic conceptual models and their features of physical parameter. The results indicate there are 4 active and 3 inactive areas of short-time heavy precipitation in Shan-Gan-Ning Region.Hourly precipitation above 80 mm could occur in both areas. Short-time heavy precipitation (over 30 mm per hour) is closely associated with special terrain such as wind ward slop of mountain and trumpet-shaped terrain. Short-time heavy precipitation is active in July and August, followed by June and September. The severe rainfall occurs mostly in late June and mid-August, and the cumulative frequency is slightly smaller in early August because of droughts season. Diurnal variation presents the bimodal distribution. Short-time heavy precipitation (over 30 mm per hour) shows the characteristic that severe precipitation tends to occur in the evening (2000—0800 BT). With the increase of precipitation intensity, that feature becomes more obvious. Spatial-temporal distribution features above are closely associated with the large-scale atmospheric circulation. All 3 kinds of synoptic conceptual model have common features in physical quantities filed: Ample of vapor, convective unstablestratification, instable energy, high 0℃ isotherm height, thick warm cloud layer, and weak wind shear. Despite common features, each model has its unique features.Trough and subtropical high pattern is the most typical type in Shan-Gan-Ning Region. This pattern has the highest value of LCL and lowest of Δθ_se(500 hPa minus 850 hPa), LI, K and CAPE, so the short-time heavy precipitation happens most frequently and the hourly precipitation is seldom more than 25 mm. Low vortex and typhoon far away pattern has the most favorable vapor condition and its deep wet area, sub-synoptic scale Ω system, lowest LCL results in broad precipitation areas and stronger precipitation. Shear between two high pressure pattern has the highest contribution of Δθ_se, LI, K, CAPE and strongest vertical wind shear (0—3 km), which leads to the most sever precipitation. Short-time heavy precipitation of this pattern occurs more suddenly and doesn't last long, when the SWEAT reaches near 300. It can also be found that the occurrence of short-time heavy precipitation is often accompanied by thunderstorm.